superset your squat/deadlift warmup / backoff sets with easy core work - just take care to drop it if you're working around your max. this is an awesome way to build up; start with a number that you can do very easily and tack on a rep every week. between my squat warmups and backoff sets i end up doing 10x8 ab wheels and it doesn't affect my squatting negatively at all. i don't know about you but i hate doing ab work after my session is done so supersetting it in means i get it done. i pretty much stick to ab wheels and hanging leg raises at this point. i've never really gotten the hang of pulldown abs and i find it too easy to cheat on situps. i think a lot of ab exercises are deceptive as lots of them "burn" but i question their actual usefulness.
also, if you're really keen and want to boost your GPP and get the heart rate up, add in 25 speed rope contacts between warmup sets, and tack on another 10-15 contacts as time goes on. before you know it you'll be knocking out 100 contacts x 10 which helps a lot with both fat loss and overall conditioning. it also warms up your rotator cuffs nicely.
the whole idea behind this supersetting stuff is to acclimatize your body to a "minimum" workload while still having it benefit from the volume you're doing. these are pretty simple methods to boost your core strength and make sure you don't get winded when you climb a flight of stairs.